Electronic device

ABSTRACT

To provide an electronic device capable of bright image display. A pixel is structured such that a switching TFT and a current controlling TFT are formed on a substrate and an EL element is electrically connected to the current controlling TFT. A gate capacitor formed between a gate electrode of the current controlling TFT and an LDD region thereof holds a voltage applied to the gate electrode, and hence a capacitor (condenser) is not particularly necessary in the pixel, thereby making the effective light emission area of the pixel large.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an electronic device having anelement that is comprised of a light emitting material sandwichedbetween electrodes, and to an electric apparatus using the electronicdevice for its display unit (display or display monitor). Specifically,the present invention relates to an electronic device using a lightemitting material that provides EL (Electro Luminescence) (Note that thematerial will hereinafter be called EL material).

[0003] 2. Description of the Related Art

[0004] In recent years, development is proceeding in an electronicdevice using a self light emitting element that utilizes the ELphenomenon of a light emitting material (hereinafter referred to as ELelement) (the device will hereafter be referred to as EL displaydevice). The EL display device is a display device that uses a selflight emitting element and, hence, unlike a liquid crystal displaydevice, does not need a backlight. In addition, the EL display devicehas a wide angle of view, which makes the device a promising candidatefor a display unit of a portable apparatus for outdoor use.

[0005] There are two kinds of EL display device: a passive type (passivematrix type) and an active type (active matrix type), and both types arebeing developed actively. However, what draws attention most is, atpresent, an active matrix type EL display device. The EL materialemitting EL and forming a light-emitting layer also is divided into twotypes, one being an organic EL material and the other being an inorganicEL material. The organic material is further divided into a lowmolecular weight type (monomer type) organic EL material and a highmolecular weight type (polymer type) organic EL material. The polymertype organic EL material is particularly highly regarded, for it iseasier to handle and has higher heat resistance in comparison with thelow molecular weight type organic EL material. Incidentally, alight-emitting device using an organic EL material is called OLED(organic light emitting diode) in Europe.

[0006] The active matrix type EL display device is characterized in thateach of pixels that constitute a pixel portion is provided with anelectric field transistor, recently, a thin film transistor (hereinafterreferred to as TFT), to control the amount of current flowing through anEL element by the TFT. As a typical pixel structure for such an activematrix type EL display device, there is known a structure illustrated inFIG. 1 attached to Japanese Patent Application Laid-open No. Hei8-241048.

[0007] The pixel structure disclosed in the publication sets twotransistors (T1, T2) in one pixel, and a capacitor (condenser: Cs) isprovided in a drain of the transistor (T1) parallel to the transistor(T2). This capacitor (condenser) is necessary for holding a voltageapplied to a gate of the transistor (T2) for one field period or oneframe period.

[0008] When two transistors and a capacitor (condenser) are formed inone pixel however, these elements occupy almost all the pixel area,causing a reduction of the effective light emission area (the area inwhich light emitted from a light-emitting layer is allowed to transmitto be used).

SUMMARY OF THE INVENTION

[0009] The present invention has been made in view of the above problem,and an object of the present invention is therefore to provide anelectronic device capable of bright image display by using a pixelstructure with a large effective light emission area. Another object ofthe present invention is to provide an electronic device of highreliability. Still another object of the present invention is to providean electric appliance using the electronic device as its display unit.

[0010] Yet still another object of the present invention is to provide aprocess for reducing the cost of manufacturing the electronic devicecapable of displaying an image with high brightness.

[0011] The present invention is characterized in that a voltage appliedto a gate of a TFT for supplying current to an EL element (hereinafterreferred to as current controlling TFT) is held by a gate capacitor(parasitic capacitor formed between the gate and an active layer) of thecurrent controlling TFT. In other words, the present invention activelyutilizes the gate capacitor of the current controlling TFT(corresponding to the transistor (T2) in FIG. 1 of Japanese PatentApplication Laid-open No. Hei 8-241048) instead of the capacitor(condenser: Cs) shown in FIG. 1 of Japanese Patent Application Laid-openNo. Hei 8-241048.

[0012] The present invention is characterized in that an LDD region isformed on a drain region side of the current controlling TFT that iscomprised of a P-channel TFT so that the LDD region overlaps with a gateelectrode through a gate insulating film sandwiched therebetween.Usually, a P-channel TFT is used without forming therein any LDD region,and thus the invention is characterized by forming the LDD region inorder to form the gate capacitor.

[0013] The structure as such practically dispenses with the area thecapacitor (condenser) occupies, thereby greatly increasing the effectivelight emission area.

[0014] The EL display devices referred to in this specification includetriplet-based light emission devices and/or singlet-based light emissiondevices.

[0015] The present invention employs a process of manufacturing aplurality of electronic devices from one large-sized substrate in orderto reduce manufacturing cost of the electronic device, namely, toproduce a low cost electronic device. The characteristic of the presentinvention resides in considerably reducing the manufacturing cost bylimiting the investment in plant and equipment to a minimum withemployment of a process to which an existing production line for liquidcrystal can be applied.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a diagram showing the cross sectional structure of thepixel portion of an electronic device of the present invention;

[0017]FIGS. 2A and 2B are diagrams showing the top structure and theconfiguration, respectively, of the pixel portion of the presentinvention;

[0018]FIGS. 3A to 3E are diagrams showing manufacturing processes of anactive matrix substrate of Embodiment 1;

[0019]FIGS. 4A to 4D are diagrams showing manufacturing processes of theactive matrix substrate of Embodiment 1;

[0020]FIGS. 5A to 5C are diagrams showing manufacturing processes of theactive matrix type substrate of Embodiment 1;

[0021]FIG. 6 is an enlarged diagram of the pixel portion of the presentinvention;

[0022]FIG. 7 is a diagram showing the circuit block structure of an ELdisplay device of Embodiment 1;

[0023]FIGS. 8A and 8B are cross sectional diagrams of an EL displaydevice of Embodiment 1;

[0024]FIGS. 9A to 9C are diagrams showing the circuit structures of anEL display device of Embodiment 2;

[0025]FIGS. 10A and 10D are cross sectional diagrams of the currentcontrol TFTs of Embodiment 3;

[0026]FIGS. 11A and 11B are diagrams showing processes of obtainingmultiple number of an EL display device of Embodiment 4;

[0027]FIGS. 12A and 12B are diagrams showing the processes of obtainingmultiple number of an EL display device of Embodiment 4;

[0028]FIGS. 13A and 13B are diagrams showing the processes of obtainingmultiple number of an EL display device of Embodiment 4;

[0029]FIGS. 14A to 14F are diagrams showing specific examples ofelectric apparatus of Embodiment 9;

[0030]FIGS. 15A and 15B are diagrams showing specific examples ofelectric apparatus of Embodiment 9; and

[0031]FIGS. 16A and 16B are photographs showing images of the EL displaydevice of Embodiment 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0032] [Embodiment Mode]

[0033] An embodiment mode of the present invention will be describedwith reference to FIG. 1 and FIGS. 2A and 2B. Shown in FIG. 1 is asectional view of a pixel portion of an EL display device according tothe present invention, and FIG. 2A is a top view thereof whereas FIG. 2Billustrates the circuit structure thereof. Actually, plural pixels arearranged in a matrix-like manner to form the pixel portion (imagedisplay portion). Common reference symbols are used in FIG. 1 and FIGS.2A and 2B. Therefore, the drawings can be cross-referred. Two pixelsshown in the top view of FIG. 2A share the same structure.

[0034] In FIG. 1, reference symbol 11 denotes a substrate and 12 denotesan insulating film that serves as a base (hereinafter referred to as abase film). Substrates usable as the substrate 11 include a glasssubstrate, a glass ceramic substrate, a quartz substrate, a siliconsubstrate, a ceramic substrate, a metal substrate, and a plasticsubstrate (including a plastic film).

[0035] The base film 12 is effective particularly when using a substratecontaining a movable ion or a substrate having a conductivity. However,the base film is not necessarily provided on a quartz substrate. Aninsulating film containing silicon is suitable for the base film 12. Theterm “an insulating film containing silicon” herein designates,specifically, an insulating film containing, in given proportions,silicon, and oxygen or nitrogen, such as a silicon oxide film, a siliconnitride film, or a silicon oxide nitride film (expressed as SiOxNy).

[0036] To give heat releasing action to the base film 12 to release heatgenerated from the TFT is also effective in preventing degradation ofthe TFT or degradation of the EL element. Any known material may be usedto impart to the base film the heat releasing action.

[0037] In FIGS. 2A and 2B, two TFTs are formed in each pixel. Referencesymbol 201 denotes a TFT functioning as a switching element (hereinafterreferred to as a switching TFT) and 202 denotes a TFT functioning as acurrent controlling element (hereinafter referred to as currentcontrolling TFT) for controlling the amount of current flowing into theEL element. The switching TFT 201 is composed of an N-channel type TFTwhereas the current controlling TFT 202 is composed of a P-channel TFT.

[0038] However, according to the present invention, the switching TFTand the current controlling TFT are not necessarily limited to the abovecombination of N-channel TFT and P-channel TFT. The switching TFT 201may be formed from a P-channel TFT, or both the switching TFT and thecurrent controlling TFT may be formed from N-channel TFTs.

[0039] The switching TFT 201 is formed to have a source region 13, adrain region 14, LDD regions 15 a to 15 d, an active layer including ahigh concentration impurity region 16 and channel forming regions 17 a,17 b, a gate insulating film 18, gate electrodes 19 a, 19 b, a firstinterlayer insulating film 20, a source wiring 21, and a drain wiring22. As shown in FIG. 2A, the gate electrodes 19 a, 19 b constitute thedouble gate structure in which a gate wiring 211 formed from a materialdifferent from a material used for forming the gate electrodes 19 a, 19b (the former material is less resistive than the latter material)electrically connects the gate electrode 19 a to the gate electrode 19b. The structure of the gate electrodes of course is not limited to thedouble gate structure, but may be a multi-gate structure (a structure inwhich a plurality of TFTs are connected in series) such as the triplegate structure.

[0040] The multi-gate structure is very effective in lowering an OFFcurrent value, and, in the present invention, the switching TFT 201 ofthe pixel takes the multi-gate structure to thereby form a switchingelement having a low OFF current value. The LDD regions 15 a to 15 d inthe switching TFT 201 are formed so as not to overlap with the gateelectrodes 19 a, 19 b through the gate insulating film 18 sandwichedthere between. This structure is very effective in lowering the OFFcurrent value.

[0041] It is even more desirable in terms of lowering the OFF currentvalue to form an offset region (a region which is formed from asemiconductor layer having the same composition as the channel formingregions and to which a gate voltage is not applied) between the channelforming regions and the LDD regions. In the case of a multi-gatestructure having two or more gate electrodes, the high concentrationregion formed between the channel forming regions is effective inlowering the OFF current value.

[0042] The OFF current value can be lowered sufficiently when the TFThaving the multi-gate structure is used for the switching TFT 201 of thepixel as described above. In other words, that the OFF current value issmall means that a voltage applied to the gate of the currentcontrolling TFT can be held longer. This provides an advantage in thatthe gate voltage of the current controlling TFT can be held until thenext writing period even when the capacitor (condenser) for holding theelectric potential, as shown in FIG. 1 of Japanese Patent ApplicationLaid-open No. Hei 8-241048, is downsized or omitted.

[0043] Next, the current controlling TFT 202 that is a P-channel TFT isformed to have a source region 31, a drain region 32, an active layerincluding an LDD region 33 and a channel forming region 34, a gateinsulating film 18, a gate electrode 35, a first interlayer insulatingfilm 20, a source wiring 36, and a drain wiring 37. The gate electrode35 has the single gate structure, but may take a multi-gate structure.

[0044] As shown in FIG. 1, the drain region 14 of the switching TFT 201is connected to the gate electrode 35 of the current controlling TFT202. To be specific, the gate electrode 35 of the current controllingTFT 202 is electrically connected through the drain wiring 22 to thedrain region 14 of the switching TFT 201. The source wiring 36 isconnected to a current supply line (also called power supply line) 212(see FIG. 2A).

[0045] The current controlling TFT 202 is an element for controlling theamount of current flowing into an EL element 203. Consideringdegradation of the EL element, it is not desirable to cause a largecurrent to flow through the EL element 203. Therefore, in order toprevent excessive current flow in the current controlling TFT 202, achannel length (L) is preferably designed to be rather long. Desirably,the channel length for one pixel is 0.5 to 2 μA (more desirably, 1 to1.5 μA).

[0046] As shown in FIG. 6, the channel length of the switching TFT isgiven as L1 (L1=L1a+L1b) and the channel width thereof as W1, whereasthe channel length of the current controlling TFT is given as L2 and thechannel width thereof as W2. Then, based on the above, W1 is preferably0.1 to 5 μm (typically 0.5 to 2 μm), W2 is preferably 0.5 to 10 μm(typically 2 to 5 μm). L1 is preferably 0.2 to 18 μm (typically 2 to 15μm), and L2 is preferably 1 to 50 μm (typically 10 to 30 μm). However,the present invention is not limited to the values above.

[0047] The length (width) of the LDD region formed in the switching TFT201 is appropriately set to 0.5 to 3.5 μm, typically 2.0 to 2.5 μm.

[0048] The EL display device shown in FIG. 1 is characterized in thatthe LDD region 33 is formed between the drain region 32 and the channelforming region 34 in the current controlling TFT 202, and that the LDDregion 33 overlaps with the gate electrode 35 through the gateinsulating film 18 sandwiched therebetween. The length of the LDD regionoverlapping with the gate electrode is appropriately set to 0.1 to 3 μm(preferably 0.3 to 1.5 μm).

[0049] The present invention is characterized by actively using, as acapacitor (condenser) for holding a voltage (for holding electriccharges), the parasitic capacitor (gate capacitor) formed between thegate electrode and the active layer that overlaps with the gateelectrode through the gate insulating film sandwiched therebetween.

[0050] In this embodiment mode, the capacitance of the gate capacitorplaced between the gate electrode 35 and the active layer (specifically,the LDD region 33) is increased by forming the LDD region 33 shown inFIG. 1, and this gate capacitor is used as a capacitor (condenser) forholding a voltage applied to the gate of the current controlling TFT202. Another capacitor may be formed separately, of course, but byadopting the structure of this embodiment mode, the area for forming thecapacitor (condenser) can be omitted to thereby increase the effectivelight emission area of the pixel.

[0051] In particular, if the EL display device of the present inventionis operated on a digital driving system, a very small capacitor(condenser) is satisfiable as the capacitor (condenser) for holding thevoltage. The capacitance thereof is, for example, about one fifth or onetenth compared to the case of an analog driving system. Though it isdifficult to present specific values in a wholesale manner because theyvary depending upon the ability of the switching TFT and the currentcontrolling TFT, 5 to 30 fF (femto-farad) will be sufficient.

[0052] If the switching TFT takes a multi-gate structure to lower theOFF current value as shown in FIG. 1, the capacitance required for thecapacitor (condenser) to hold the voltage is further reduced. Thereforeno problem is caused by the structure in which only the gate capacitoris used as the capacitor (condenser) for holding the voltage as shown inFIG. 1.

[0053] Although the current controlling TFT 202 has the single gatestructure in this embodiment mode, it may take a multi-gate structure inwhich a plurality of TFTs are connected in series. Alternatively, it maybe a structure capable of radiating heat with high efficiency, in whicha plurality of TFTs are connected parallel to each other tosubstantially divide the channel forming region into plural sections.This is an effective structure as a countermeasure against degradationby heat.

[0054] Reference symbol 38 denotes a first passivation film with a filmthickness of 10 nm to 1 μm (preferably 200 to 500 nm). An insulatingfilm containing silicon (a silicon oxide nitride film or a siliconnitride film is particularly preferable) can be used as a material ofthe first passivation film. It is effective to impart heat releasingaction to the first passivation film 38.

[0055] A second interlayer insulating film (planarizing film) 39 isformed on the first passivation film 38 to level out a level differencecaused by the TFT. A preferred material for the second interlayerinsulating film 39 is an organic resin film, and a polyimide film, apolyamide film, an acrylic resin film, a BCB (benzocyclobuten) film,etc., are appropriate. Of course, an inorganic film may be used if itcan satisfiably level out the level difference.

[0056] It is very important to level out the level difference caused bythe TFT using the second interlayer insulating film 39. The EL layer tobe formed later is so thin that the existence of a level difference maylead to inferior light emission. Therefore planarization beforeformation of a pixel electrode is required, so that the EL layer can beformed on a surface as flat as possible.

[0057] Denoted by reference symbol 40 is a pixel electrode formed from atransparent conductive film (anode of the EL element). The pixelelectrode is formed by opening a contact hole (aperture) piercingthrough the second interlayer insulating film 39 and the firstpassivation film 38, and then being brought into contact, in the thusformed aperture, with the drain wiring 37 of the current controlling TFT202. A conductive film mainly containing a compound of indium oxide andtin oxide or a compound of indium oxide and zinc oxide is preferablyused as the pixel electrode 40. The conductive film may of course belayered on another transparent conductive film to form a laminatestructure.

[0058] Next, an EL material is formed into a light-emitting layer 42.Although both the inorganic EL material and the organic EL material maybe used as the EL material for the light-emitting layer, the organic ELmaterial that is low in drive voltage is preferred. As the organic ELmaterial, both the low molecular weight type (monomer type) organic ELmaterial and the high molecular weight type (polymer type) organic ELmaterial may be used.

[0059] Representative monomer type organic EL material are Alq₃(8-hydroquinoline aluminum) and DSA (distyryl arylene derivative). Anyknown material other than these may also be used.

[0060] Polyparaphenylene vinylene (PPV), polyvinyl carbazole (PVK),etc., are named as an example of the polymer type organic EL material.Any known material may also be used, of course. Specifically, preferredarrangement is such that cyanopolyphenylene vinylene is used for alight-emitting layer that emits red light, polyphenylene vinylene for alight-emitting layer that emits green light, and polyphenylene vinyleneor polyalkylphenylene for a light-emitting layer that emits blue light.An appropriate film thickness thereof is 30 to 150 nm (preferably 40 to100 nm).

[0061] The light-emitting layer may be doped with a fluorescentsubstance (typically, coumarin 6, rubrene, Nile red, DCM, quinacridone,etc.) to shift the luminescence center to the fluorescent substance andobtain light emission as desired. Any known fluorescent substance may beused.

[0062] If the monomer type organic EL material is used as thelight-emitting layer 42, the layer is formed by vacuum evaporation. Onthe other hand, spin coating, printing, the ink jet method, ordispensing is employed to form the light-emitting layer 42 from thepolymer type organic EL material. When forming the layer from thepolymer type organic EL material, however, the processing atmosphere isdesirably a dry inert atmosphere that contains moisture in as smallamount as possible. In this embodiment mode, the layer is formed fromthe polymer type organic EL material by spin coating.

[0063] The polymer type organic EL material is formed into thelight-emitting layer under normal pressure. However, the organic ELmaterial is easily degraded in the presence of moisture and oxygen.These degradation factors therefore must be removed as much as possiblefrom the processing atmosphere when forming the EL material into thelayer. Preferred atmosphere is, for example, dry nitrogen atmosphere,dry argon atmosphere, and the like. Accordingly, it is desirable toplace an apparatus for forming the light-emitting layer in a clean boothfilled with an inert gas and conduct the step of forming thelight-emitting layer in the inert atmosphere.

[0064] After thus forming the light-emitting layer 42, then an electroninjection layer 43 is formed. A monomer type organic material such aslithium fluoride or acetylacetonate complex is used for the electroninjection layer 43. A polymer type organic material or an inorganicmaterial may also be used, of course. An appropriate film thicknessthereof is 3 to 20 nm (preferably, 5 to 15 nm).

[0065] It should be noted that the materials mentioned above are merelyexemplary of organic materials usable as the light-emitting layer or theelectron injection layer of the present invention, and that there is noneed to limit the layer materials thereto. Also note that, though shownhere is a combination of the light-emitting layer and the electroninjection layer, the light-emitting layer may be combined with a holetransportation layer, a hole injection layer, an electron transportationlayer, a hole blocking layer, or an electron blocking layer.

[0066] Provided on the electron injection layer 43 is a cathode 44formed from a conductive film having a small work function. As theconductive film having a small work function, an aluminum alloy film, acopper alloy film, or a silver alloy film may be used. A laminate filmconsisting of any of the alloy films mentioned above and anotherconductive film may be used as well. The cathode 44 also serves as apassivation film for protecting the organic EL material in thelight-emitting layer and other layers from oxygen and moisture.

[0067] Upon formation of the cathode 44, the EL element 203 iscompleted. The EL element 203 here is a capacitor (condenser) composedof the pixel electrode (anode) 40, the light-emitting layer 42, theelectron injection layer 43, and the cathode 44. In this embodimentmode, the light emitted from the light-emitting layer 42 is transmittedthrough the substrate 11 to be used, and hence a part of the pixel whichis not occupied by the TFT corresponds to the effective light-emissionarea. According to the present invention, the capacitor (condenser) forholding the gate voltage of the current controlling TFT 202 is takencare of by the current controlling TFT 202 with its own gate capacitor.The effective light emission area is thus wide, making it possible toprovide bright image display.

[0068] Though shown in this embodiment mode is the structure of a planartype TFT as an example of using a top gate type TFT, a bottom gate typeTFT (typically, an inverted stagger type TFT) may also be used.

[0069] [Embodiment 1]

[0070] The embodiments of the present invention are explained usingFIGS. 3A to 5C. A method of simultaneous manufacture of a pixel portion,and TFTs of a driver circuit portion formed in the periphery of thepixel portion; is explained here. Note that in order to simplify theexplanation, a CMOS circuit is shown as a basic circuit for the drivercircuits.

[0071] First, as shown in FIG. 3A, a base film 301 is formed with a 300nm thickness on a glass substrate 300. Silicon nitride oxide films arelaminated as the base film 302 in this embodiment. It is good to set thenitrogen concentration at between 10 and 25 wt % in the film contactingthe glass substrate 300. Further, it is advantageous to provide the basefilm with a heat radiation function, a DLC (diamond like carbon) filmcan also be provided.

[0072] Next, an amorphous silicon film (not shown in the figures) isformed with a thickness of 50 nm on the base film 301 by a knowndeposition method. Note that it is not necessary to limit this to theamorphous silicon film, and another film may be formed provided that itis a semiconductor film containing an amorphous structure (including amicrocrystalline semiconductor film). In addition, a compoundsemiconductor film containing an amorphous structure, such as anamorphous silicon germanium film, may also be used. Further, the filmthickness may be made from 20 to 100 nm.

[0073] The amorphous silicon film is then crystallized by a knownmethod, forming a crystalline silicon film (also referred to as apolycrystalline silicon film or a polysilicon film) 302. Thermalcrystallization using an electric furnace, laser annealingcrystallization using a laser, and lamp annealing crystallization usingan infrared lamp exist as known crystallization methods. Crystallizationis performed in this embodiment using light from an excimer laser whichuses XeCl gas.

[0074] Note that pulse emission type excimer laser light formed into alinear shape is used in this embodiment, but a rectangular shape mayalso be used, and continuous emission argon laser light and continuousemission excimer laser light can also be used. Further, the firstharmonic laser to the forth harmonic laser of YAG laser can also beused.

[0075] Next, as shown in FIG. 3B, a protecting film 303 is formed on thecrystalline silicon film 302 with a silicon oxide film having athickness of 130 nm. This thickness may be chosen within the range of100 to 200 nm (preferably between 130 and 170 nm). Furthermore, otherfilms may also be used providing that they are insulating filmscontaining silicon. The protecting film 303 is formed so that thecrystalline silicon film is not directly exposed to plasma duringaddition of an impurity, and so that it is possible to have delicateconcentration control of the impurity.

[0076] Resist masks 304 a and 304 b are then formed, and an impurityelement which imparts n-type conductivity (hereafter referred to as ann-type impurity element) is added via the protecting film 303. Note thatelements residing in periodic table group 15 are generally used as then-type impurity element, and typically phosphorus or arsenic can beused. Note that a plasma doping method is used, in which phosphine (PH₃)is plasma activated without separation of mass, and phosphorus is addedat a concentration of 1×1018 atoms/cm³ in this embodiment. An ionimplantation method, in which separation of mass is performed, may alsobe used, of course.

[0077] The dose amount is regulated so that the n-type impurity elementis contained in n-type impurity regions 305, thus formed by thisprocess, at a concentration of 2×10¹⁶ to 5×10⁹ atoms/cm³ (typicallybetween 5×10¹⁷ and 5×10¹⁸ atoms/cm³).

[0078] Next, resist masks 306 a and 306 b are then formed, and animpurity element which imparts p-type conductivity (hereafter referredto as a p-type impurity element) is added via the protecting film 303.Note that elements residing in periodic table group 13 are generallyused as the p-type impurity element, and typically, boron or gallium canbe used. Note that a plasma doping method is used, in which diborane(B₂H₆) is plasma activated without separation of mass in thisembodiment. An ion implantation method, in which separation of mass isperformed, may also be used, of course. (See FIG. 3C)

[0079] The dose amount is regulated so that the p-type impurity elementis contained in p-type impurity regions 307 and 308, thus formed by thisprocess, at a concentration of 1×10¹⁵ to 5×10¹⁷ atoms/cm³ (typicallybetween 1×10¹⁶ and 1×10¹⁷ atoms/cm³). The p-type impurity element isused to regulate the threshold voltage of n-channel type TFT.

[0080] Next, the protecting film 303 is removed, and an activation ofthe added n-type impurity elements and p-type impurity elements isperformed. A known technique of activation may be used as the means ofactivation, and activation is done in this embodiment by irradiation ofexcimer laser light. A pulse emission type excimer laser and acontinuous emission type excimer laser may both, of course, be used, andit is not necessary to place any limits on the use of excimer laserlight. The purpose is the activation of the added impurity element, andit is preferable that irradiation is performed at an energy level atwhich the crystalline silicon film does not melt. Note that the laserirradiation may also be performed with the protecting film 303 in place.

[0081] The activation by heat treatment may also be performed along withactivation of the impurity element by laser light. When activation isperformed by heat treatment (furnace annealing), considering the heatresistance of the substrate, it is good to perform heat treatment on theorder of 450 to 550° C.

[0082] Unnecessary portions of the crystalline silicon film are removednext, as shown in FIG. 3D, and island shape semiconductor films(hereafter referred to as active layers) 309 to 312 are formed.

[0083] Then, as shown in FIG. 3E, a gate insulating film 313 is formed,covering the active layers 309 to 312. An insulating film containingsilicon and with a thickness of 10 to 200 nm, preferably between 50 and150 nm, may be used as the gate insulating film 313. A single layerstructure or a lamination structure may be used. A 110 nm thick siliconnitride oxide film is used in this embodiment.

[0084] A conducting film with a thickness of 200 to 400 nm is formednext and patterned, forming gate electrodes 314 to 318. Note that inthis embodiment, the gate electrodes and lead wirings electricallyconnected to the gate electrodes (hereafter referred to as gate wirings)are formed from different materials. Specifically, a material having alower resistance than that of the gate electrodes is used for the gatewirings. This is because a material which is capable of beingmicro-processed is used as the gate electrodes, and even if the gatewirings cannot be micro-processed, the material used for the wirings haslow resistance. Of course, the gate electrodes and the gate wirings mayalso be formed from the same material.

[0085] Further, the gate wirings may be formed by a single layerconducting film, and when necessary, it is preferable to use a two layeror a three layer lamination film. All known conducting films can be usedas the gate electrode material. However, as stated above, it ispreferable to use a material which is capable of being micro-processed,specifically, a material which is capable of being patterned to a linewidth of 2 μm or less.

[0086] Typically, it is possible to use a film made of an elementselected from tantalum (Ta), titanium (Ti), molybdenum (Mo), tungsten(W), chromium (Cr), and silicon (Si), a film of nitride of the aboveelement (typically a tantalum nitride film, tungsten nitride film, ortitanium nitride film), an alloy film of combination of the aboveelements (typically Mo—W alloy, Mo—Ta alloy), or a silicide film of theabove element (typically a tungsten silicide film, titanium silicidefilm). Of course, the films may be used as a single layer or a laminatelayer.

[0087] In this embodiment, a laminate film of a tungsten nitride (WN)film having a thickness of 30 nm and a tungsten (W) film having athickness of 370 nm is used. These may be formed by a sputtering method.When an inert gas of Xe, Ne or the like is added as a sputtering gas,film peeling due to stress can be prevented.

[0088] The gate electrodes 315 and 318 are formed at this time so as tooverlap and sandwich a portion of the n-type impurity regions 305, apart of p-type impurity region 308, and the gate insulating film 313respectively. This overlapping portion later becomes an LDD regionoverlapping the gate electrode.

[0089] Next, an n-type impurity element (phosphorus is used in thisembodiment) is added in a self-aligning manner with the gate electrodes314 to 318 as masks, as shown in FIG. 4A. The addition is regulated sothat phosphorus is added to impurity regions 319 to 326 thus formed at aconcentration of {fraction (1/10)} to ½ that of the n-type impurityregions 305 (typically between ¼ and ⅓). Specifically, a concentrationof 1×10¹⁶ to 5×10¹⁸ atoms/cm³ (typically 3×10¹⁷ to 3×10¹⁸ atoms/cm³) ispreferable.

[0090] Resist masks 327 a to 327 d are formed next, with a shapecovering the gate electrodes etc, as shown in FIG. 4B, and an n-typeimpurity element (phosphorus is used in this embodiment) is added,forming impurity regions 328 to 332 containing a high concentration ofphosphorus. Ion doping using phosphine (PH₃) is also performed here, andis regulated so that the phosphorus concentration of these regions isfrom 1×10²⁰ to 1×10²¹ atoms/cm³ (typically between 2×10²⁰ and 5×10²⁰atoms/cm³).

[0091] A source region or a drain region of the n-channel TFT is formedby this process, and in the switching TFT, a portion of the n-typeimpurity regions 322 to 324 formed by the process of FIG. 4A remains.These remaining regions correspond to the LDD regions 15 a to 15 d ofthe switching TFT in FIG. 1.

[0092] Next, as shown in FIG. 4C, the resist masks 327 a to 327 d areremoved, and a new resist mask 333 is formed. A p-type impurity element(boron is used in this embodiment) is then added, forming impurityregions 334 to 337 containing a high concentration of boron. Boron isadded here at a concentration of 3×10²⁰ to 3×10²¹ atoms/cm³ (typicallybetween 5×10²⁰ and 1×10²¹ atoms/cm³) by ion doping using diborane(B₂H₆).

[0093] Note that phosphorus has already been added to the impurityregions 334 to 337 at a concentration of 1×10¹⁶ to 5×10¹⁸ atoms/cm³, butboron is added here at a concentration of at least 3 times than of thephosphorus. Therefore, the n-type impurity regions already formedcompletely invert to p-type, and function as p-type impurity regions.

[0094] Next, after removing the resist mask 333, the n-type and p-typeimpurity elements added at various concentrations are activated. Furnaceannealing, laser annealing, or lamp annealing may be performed as ameans of activation. Heat treatment is performed in this embodiment in anitrogen atmosphere for 4 hours at 550° C. in an electric furnace.

[0095] It is important to remove as much of the oxygen in the atmosphereas possible at this time. This is because if any oxygen exists, then theexposed surface of the electrode is oxidized, inviting an increase inresistance, and at the same time it becomes more difficult to later makean ohmic contact. It is therefore preferable that the concentration ofoxygen in the processing environment in the above activation processshould be 1 ppm or less, desirably 0.1 ppm or less.

[0096] After the activation process is completed, a gate wiring 338 witha thickness of 300 nm is formed next. A metallic film having aluminum(Al) or copper (Cu) as its principal constituent (comprising 50 to 100%of the composition) may be used as the material of the gate wiring 338.As with the gate wiring 211 of FIGS. 2A and 2B, the gate wiring 338 isformed with a placement so that the gate electrodes 316 and 317 of theswitching TFTs (corresponding to gate electrodes 19 a and 19 b ofFIG. 1) are electrically connected. (See FIG. 4D.)

[0097] The wiring resistance of the gate wiring can be made extremelysmall by using this type of structure, and therefore a pixel displayregion (pixel portion) having a large surface area can be formed.Namely, the pixel structure of this embodiment is extremely effectivebecause an EL display device having a screen size of a 10 inch diagonalor larger (in addition, a 30 inch or larger diagonal) is realized due tothis structure.

[0098] A first interlayer insulating film 339 is formed next, as shownin FIG. 5A. A single layer insulating film containing silicon is used asthe first interlayer insulating film 339, while a lamination film may becombined in between. Further, a film thickness of between 400 nm and 1.5μm may be used. A lamination structure of an 800 nm thick silicon oxidefilm on a 200 nm thick silicon nitride oxide film is used in thisembodiment.

[0099] In addition, heat treatment is performed for 1 to 12 hours at 300to 450° C. in an environment containing between 3 and 100% hydrogen,performing hydrogenation. This process is one of hydrogen termination ofdangling bonds in the semiconductor film by hydrogen which is thermallyactivated. Plasma hydrogenation (using hydrogen activated by a plasma)may also be performed as another means of hydrogenation.

[0100] Note that the hydrogenation step may also be inserted during theformation of the first interlayer insulating film 339. Namely, hydrogenprocessing may be performed as above after forming the 200 nm thicksilicon nitride oxide film, and then the remaining 800 nm thick siliconoxide film may be formed.

[0101] Next, a contact hole is formed in the first interlayer insulatingfilm 339, and source wiring lines 340 to 343 and drain wiring lines 344to 346 are formed. In this embodiment, this electrode is made of alaminate film of three-layer structure in which a titanium film having athickness of 100 nm, an aluminum film containing titanium and having athickness of 300 nm, and a titanium film having a thickness of 150 nmare continuously formed by a sputtering method. Of course, otherconductive films may be used.

[0102] A first passivation film 347 is formed next with a thickness of50 to 500 nm (typically between 200 and 300 nm). A 300 nm thick siliconnitride oxide film is used as the first passivation film 347 in thisembodiment. This may also be substituted by a silicon nitride film. Notethat it is effective to perform plasma processing using a gas containinghydrogen such as H₂ or NH₃ etc. before the formation of the siliconnitride oxide film. Hydrogen activated by this preprocess is supplied tothe first interlayer insulating film 339, and the film quality of thefirst passivation film 347 is improved by performing heat treatment. Atthe same time, the hydrogen added to the first interlayer insulatingfilm 339 diffuses to the lower side, and the active layers can behydrogenated effectively.

[0103] Next, as shown in FIG. 5B, a second interlayer insulating film348 made of organic resin is formed. As the organic resin, it ispossible to use polyimide, polyamide, acryl, BCB (benzocyclobutene) orthe like. Especially, since the second interlayer insulating film 348 isprimarily used for flattening, acryl excellent in flattening propertiesis preferable. In this embodiment, an acrylic film is formed to athickness sufficient to flatten a stepped portion formed by TFTs. It isappropriate that the thickness is preferably made 1 to 5 μm (morepreferably, 2 to 4 μm).

[0104] A contact hole reaching a drain wiring line 346 is formed throughthe second interlayer insulating film 348, and the first passivationfilm 347, and a pixel electrode 349, which is made of transparentconductive film, is formed. In this embodiment, a conductive film havinga thickness of 120 nm is formed, which is made of combined element ofindium-tin oxide and zinc oxide, as a pixel electrode 349.

[0105] Next, an insulating film 350 is formed as shown in FIG. 5C. Theinsulating film 350 is formed by patterning the organic resin film orthe insulating film contains 100-300 nm silicon. This insulating film350 is formed to fill the space between pixels (pixel electrodes). Thisinsulating film 350 is formed for organic EL material, which is formednext, of luminescence layer not to overlap the edge portion of pixelelectrode 349.

[0106] A light emitting layer 351 is next formed by the spin coatingmethod. Specifically, an organic EL material that becomes the lightemitting layer 351 is dissolved in a solvent such as chloroform,dichloromethane, xylene, toluene, and tetrahydrofuran, and is thenapplied. Thereafter, heat treatment is performed to volatilize thesolvent. A film (light emitting layer) made of the organic EL materialis thus formed. In this embodiment, a paraphenylene vinylene is used forthe light emitting layer emitting green color. The light emitting layeris formed to a thickness of 50 nm. In addition, 1.2 dichloromethane isused as a solvent, and then volatilized by performing heat treatment ona hot plate at 80 to 150° C. for 1 minute.

[0107] Next, an electron injection layer 352 is formed to a thickness of20 nm. As an electron injection layer 352, lithium fluoride is formed bythe evaporation. As an electron injection layer 352, other polymerorganic material and monomer organic material can be used. The inorganicmaterial can also be used.

[0108] A two-layered structure made of the light emitting layer and theelectron injection layer is formed in Embodiment 1. However, otherlayers such as a hole transporting layer, a hole injection layer, and anelectron transporting layer may also be provided. Examples of variouslamination structures of such combination of layers have been reported,and any structure may be used for the present invention.

[0109] After the formation of the light emitting layer 351 and theelectron injection layer 352, an cathode 353 made of a small workfunction transparent conductive film is formed to a thickness of 350 nm.In this embodiment, an alloy of lithium and aluminum is formed by vacuumevaporation method.

[0110] An active matrix substrate having a structure as shown in FIG. 5Cis thus completed. Note that after the formation of the insulating film350, it is effective to use the multi-chamber method (or the in-linemethod) of the thin film deposition apparatus for the process of formingthe films until the formation of the cathode 353, in succession andwithout exposure to the atmosphere.

[0111] In the active matrix substrate of this embodiment, TFTs havingoptimal structures are arranged not only in the pixel portion but alsoin the driver circuit portion, thereby indicating an extremely highreliability and increasing its operation performance.

[0112] First, a TFT having a structure to decrease hot carrier injectionso as not to drop the operation speed thereof as much as possible isused as an n-channel TFT 205 of a CMOS circuit forming a driver circuitportion. Note that the driver circuit here includes a shift register, abuffer, a level shifter, a sampling circuit (sample and hold circuit), aD/A converter and the like.

[0113] In the case of this embodiment, as shown in FIG. 5C, an activelayer of the n-channel TFT 205 is composed of a source region 355, adrain region 356, an LDD region 357, and a channel forming region 358.The LDD region 357 overlaps the gate electrode 315 via the gateinsulating film 313.

[0114] Consideration not to drop the operation speed is the reason whythe LDD region is formed at only the drain region side. In thisn-channel TFT 205, it is not necessary to pay attention to an OFFcurrent value very much, rather, it is better to give importance to anoperation speed. Thus, it is desirable that the LDD region 357 is madeto completely overlap the gate electrode to decrease a resistancecomponent to a minimum.

[0115] The p-channel TFT 206 in the CMOS circuit includes the sourceregion 334, the drain region 335 and the channel formation region 359.Furthermore, deterioration due to the injection of hot carriers isalmost negligible, and thus, it is not necessary to provide any LDDregion however it is also possible to provide it.

[0116] Note that, in practice, it is preferable to additionally performpackaging (sealing) after completing up through FIG. 5C by using ahighly airtight protective film which has very little gas leakage (suchas a laminate film or an ultraviolet cured resin film) or a sealingmaterial that is transmissive, so that there is no exposure to theatmosphere. By making the surrounded portion by the sealing material aninert environment, an inert liquid material and an inert solid materialand by placing a drying agent (for example, barium oxide) within thesealing material, the reliability of the EL element is increased.

[0117] Furthermore, after the airtightness is increased by the packingprocessing etc., a connector (a flexible printed circuit, FPC) forconnecting output terminals from elements or circuits formed on thesubstrate and external signal terminals, is attached, completing anelectronic device using EL element. The electronic device of thisspecification includes a connector for input a signal from outside andintegral circuit which is connected to the connector.

[0118] Here, the structure of the EL display device of this embodimentwill be described with reference in FIG. 7. The EL display device ofthis embodiment is constituted by a source side driver circuit 701, apixel portion 708, and a gate side driver circuit 709. Further, in thisembodiment, the driver circuit portion is a general term including thesource side driver circuit and the gate side driver circuit.

[0119] In this embodiment, an n-channel TFT having multi-gate structureis provided as a switching TFT in the pixel portion 708, the switchingTFT is arranged to the intersection of gate wiring and source wiringwhich are connected to the gate side driver circuit 709 and the sourceside driver circuit 701 respectively. Further, the drain region of theswitching TFT is connected to the gate electrode of p-channel typecurrent control TFT electrically.

[0120] The source side driver circuit 701 is provided with a shiftregister 702, a buffer 703, a latch (A) 704, a buffer 705, a latch (B)706 and a buffer 707. Further, in the case of analog driver, thesampling circuit is provided instead of a latch (A) and a latch (B). Thegate side driver circuit 709 is provided with a shift register 710, anda buffer 711.

[0121] Further, not shown in the figure, the gate side driver circuitcan be provided at the opposite side of the gate driver circuit 709 viathe pixel portion 708. In this case, the both side own jointly gatewirings in the same structure. The structure is if the one is destroyed,the other one send a gate signal to operate a pixel portion correctly.

[0122] The foregoing structure can be easily realized by manufacturingTFTs in accordance with the manufacturing processes shown in FIGS. 3A to5C. In this embodiment, although only the structure of the pixel portionand the driver circuit portion is shown, if the manufacturing processesof this embodiment are used, it is possible to form a logical circuit,such as a signal dividing circuit, a D/A converter circuit, anoperational amplifier circuit, a γ-correction circuit, on the samesubstrate, and further, it is considered that a memory portion, amicroprocessor, or the like can be formed.

[0123] Furthermore, an explanation of the EL display device of thisembodiment, containing the sealing material to protect an EL element, ismade using FIGS. 8A and 8B. Note that, when necessary, the referencesymbols used in FIG. 7 is cited.

[0124]FIG. 8A is a diagram showing the top view of a state of completesealing process to protect an EL element. Indicated by dotted lines,reference numeral 708 denotes a pixel portion, 709 denotes a gate sidedriver circuit, and 701 denotes a source side driver circuit. Referencenumeral 801 denotes a cover material, 802 denotes a first seal member,803 denotes a second seal member and a filling material (not shown inthe figure) is provided between an active matrix substrate and a portioncover material 801 which is enclosed by the first seal member 802.

[0125] Further, reference numeral 804 denotes a connection wiring totransmit the signal which is input to the source side driver circuit 701and the gate side driver circuit 709. The connection wiring accepts avideo signal and clock signal from an outside input terminal FPC 805.

[0126] Here, the cross-sectional view taken along line A-A′ of FIG. 8Ais shown in FIG. 8B. It is to be noted that the same reference numeralsare used for the same components in FIGS. 8A and 8B.

[0127] As shown in FIG. 8B, the pixel portion 708 and the gate sidedriver circuit 709 are formed on the glass substrate 806. The pixelportion 708 is formed of a plurality of pixels containing the currentcontrol TFT 202 and the pixel electrode 349 which is electricallyconnected to the drain region of the current control TFT 202. Further,the gate side driver circuit 709 is formed by using a CMOS circuit thatis a complementary combination of the n-channel TFT 205 and thep-channel TFT 206.

[0128] The pixel electrode 349 functions as the anode of the EL element.In addition, the insulating film 350 is formed on both ends of the pixelelectrode 349, and the light emitting layer 351 and the electroninjection layer 352 are formed. The cathode 353 of the EL element isfurther formed on the top.

[0129] In the case of this embodiment, the cathode 353 also functions asa common wiring to all the pixels, and is electrically connected to theFPC 805 through the connection wiring 804. Furthermore, all the elementscontained in the pixel portion 708 and the gate side driver circuit 709are covered by the cathode 353. The cathode 353 has a function as aconnection wiring but also a passivation film to protect an EL elementfrom water and oxygen, and as a electric field shielding film.

[0130] Next, after forming a first seal member 802 by a dispenser,scattering a spacer (not shown in figure) to attach a cover material801. The spacer is scattered to maintain the distance between an activematrix substrate and cover material 801. And, the filling material 807is filled inside of the first seal member 802 by a vacuum injectingmethod. The technique, which is used in a cell assembling process ofliquid crystal display, can be used to foregoing process. It ispreferable to use a photo curing resin as the first seal member 802, buta thermally curable resin may also be used provided that the thermalresistance of the EL layer permits. Note that it is preferable that thefirst seal member 802 be a material through which as little moisture andoxygen as possible are transmitted. Further, a drying agent may also beadded to the inside of the first seal member 802.

[0131] Next, a filling material 807 is provided so as to cover the ELelement. The filling material 807 also functions as an adhesive forattaching the cover material 801. As the filling material 807,polyimide, acryl, PVC (polyvinyl chloride), epoxy resins, siliconeresins, PVB (polyvinyl butyral) or EVA (ethylene vinyl acetate) can beused.

[0132] It is preferable to place a drying agent (not shown in thefigure) inside the filling material 807 because the absorbent effect canbe maintained. At this point, the drying agent may be an agent dopedinto the filling material, or an agent enclosed in the filling material.Further, as above-mentioned spacer (not shown in the figure), it iseffective to use an absorbent material.

[0133] Further, in this embodiment, a glass plate, a quartz plate, aplastic plate, a ceramic plate, an FRP (Fiberglass-Reinforced Plastics)plate, PVF (polyvinyl fluoride) film, a Mylar film, a polyester film, oran acrylic film can be used as the cover material 801.

[0134] After using the filling material 807 to attach the cover material801, the second seal member 803 is next formed so as to cover a sidesurface (the exposed surface) of the first seal member 802. The secondseal member 803 can use the same material as the first seal member 802.

[0135] The EL element is thus sealed into the filling material 807 byusing the above procedure, to thereby completely cut off the EL elementfrom the external atmosphere and to prevent the penetration ofsubstances such as moisture and oxygen from the outside which stimulatethe deterioration of the EL element due to the oxidation of the ELlayer. Accordingly, highly reliable EL display devices can bemanufactured.

[0136] [Embodiment 2]

[0137] In this embodiment, an example of a case in which a pixelconstitution shown in FIG. 9 differs from that of the circuit diagram(constitution) shown in FIG. 2B. Note that in this embodiment, referencenumeral 901 denotes source wiring of a switching TFT 902, 903 denotes agate wiring of a switching TFT 902, 904 denotes a current control TFT,905 denotes a capacitor, 906 and 908 denote electric current supplylines, and 907 denotes an EL element.

[0138] It is to be noted that the capacitor 905 employs a gatecapacitance of the current control TFT 904. Substantially, the capacitor905 is not provided, and therefore it is indicated by a dotted line.

[0139]FIG. 9A is an example of a case in which the electric currentsupply line 906 is common between two pixels. Namely, this ischaracterized in that the two pixels are formed having linear symmetryaround the electric current supply line 906. In this case, the number ofthe electric current supply line can be reduced, and therefore the pixelportion can be made with higher definition.

[0140] Further, FIG. 9B is an example of a case in which the electriccurrent supply line 908 is formed parallel to the gate wiring 903. InFIG. 9B, the structure is formed such that the electric current supplyline 908 and the gate wiring 903 not to overlap. However, forming bothin different layers, the films can be located overlapping each otherwith an insulating film therebetween. In this case, the exclusivesurface area can be shared by the electric current supply line 908 andthe gate wiring 903, and the pixel portion can be made with higherdefinition.

[0141] Furthermore, FIG. 9C is characterized in that the electriccurrent supply line 908 and the gate wiring 903 a, 903 b are formed inparallel, similar to the structure of FIG. 9B, and additionally, in thatthe two pixels are formed so as to have linear symmetry around theelectric current supply line 908. In addition, it is effective to formthe electric current supply line 908 so as to overlap with one of thegate wirings 903 a, 903 b. In this case, the number of electric currentsupply lines can be reduced, and therefore the pixel portion can be madewith higher definition.

[0142] In addition, it is effective to employ the EL display devicehaving the pixel structure of this embodiment as the display portion ofthe electronic equipment of Embodiment 1.

[0143] [Embodiment 3]

[0144] In this embodiment, examples in which the element structure ofthe electric current controlling TFT 202 shown in FIG. 1 is made adifferent one, will be described with reference to FIGS. 10A to 10D.Specifically, examples in which the arrangement of the LDD region ismade a different one, will be described. Incidentally, the same portionsas those of the electric current controlling TFT 202 shown in FIG. 1 aredesignated by the same symbols.

[0145] An electric current controlling TFT 202A shown in FIG. 10A is anexample in which the LDD region 33 is omitted from the electric currentcontrolling TFT 202 shown in FIG. 1. In the case shown in FIG. 1, sincethe switching TFT 201 has a triple-gate structure, an off current valueis very small, and if a digital driving system is used, the capacitanceof a capacitor for holding the electric potential of the gate of theelectric current controlling TFT 202A may be very small.

[0146] Thus, as shown in FIG. 10A of this embodiment, it is possible tohold the electric potential of the gate of the electric currentcontrolling TFT 202A only by a gate capacitance formed between a gateelectrode 35 and a drain region 32.

[0147] Next, an electric current controlling TFT 202B shown in FIG. 10Bis an example in which a gate electrode 35 overlaps with a part of anLDD region 51 through a gate insulating film. In this case, a portion ofthe LDD region 51 not overlapping with the gate electrode 35 functionsas a resistor so that it has an effect of decreasing the off currentvalue. That is, by making the structure of FIG. 10B, it is possible torealize lowering of the off electric current value.

[0148] Next, an electric current controlling TFT 202C shown in FIG. 10Cis an example in which the LDD region 51 shown in FIG. 10B is providedat not only the side of the source region 31 but also at the side of thedrain region 32. In this embodiment, an additional region is made an LDDregion 52. Such a structure is an effective structure in the case wherethe direction of flow of electrons is changed (source region and drainregion are inverted) like a sampling circuit used in an analog drivingsystem.

[0149] Thus, it is also possible to use the structure of FIG. 10C for aswitching TFT. Also in that case, it is possible to realize both thesuppression of deterioration due to the hot carrier injection and thelowering of the off current value at the same time.

[0150] Next, an electric current controlling TFT 202D shown in FIG. 10Dis an example in which the LDD region 33 shown in FIG. 1 is provided atboth the side of the source region 31 and the side of the drain region32. In this embodiment, an additional region is made an LDD region 53.Such a structure is an effective structure in the case where thedirection of flow of electrons is changed like a sampling circuit usedin an analog driving system.

[0151] Incidentally, any of the structures of this embodiment can besubstituted for the electric current controlling TFT 202 of theembodiment 1, and can also be combined with the embodiment 2.

[0152] [Embodiment 4]

[0153] In this embodiment, a description will be made on a case where aplurality of EL display devices of the present invention are fabricatedby using a large substrate (large wafer). Top views of FIGS. 11A to 13Bare used for the description. Incidentally, sectional views taken alongline A-A′ and B-B′ are also shown in the respective top views.

[0154]FIG. 11A is a view showing a state where a seal member is formedon an active matrix substrate fabricated in the embodiment 1. Referencenumeral 61 designates the active matrix substrate, and first sealmembers 62 are provided at plural places. The first seal member 62 isformed while an opening portion 63 is secured.

[0155] A filler (rod-like spacer) may be added in the first seal member62. Besides, spherical spacers 64 are sprinkled on the whole activematrix substrate 61. The spacers 64 may be sprinkled before or afterformation of the first seal member 62. In either case, it is possible tosecure the distance between the active matrix substrate 61 and a covermember over the active matrix substrate 61 by the filler (not shown) orthe spacers 64.

[0156] Incidentally, in view of suppression of deterioration of the ELelement, it is effective to make the spacer 64 have a hygroscopicproperty. Besides, it is desirable that the spacer 64 is made of amaterial transmitting light emitted from the light emitting layer.

[0157] A pixel portion and a driving circuit portion are included in aregion 65 surrounded by the seal member 62. In this specification, aportion constituted by the pixel portion and the driving circuit portionis called an active matrix portion. That is, the active matrix substrate61 is formed such that a plurality of active matrix portions each beingmade of a combination of the pixel portion and the driving circuitportion are formed on one large substrate.

[0158]FIG. 11B shows a state where a cover member 66 is bonded to theactive matrix substrate 61. In this specification, a cell including theactive matrix substrate 61, the first seal member 62, and the covermember 66 is called an active matrix cell.

[0159] A process similar to a cell assembling step of liquid crystal maybe used for the above bonding. Besides, as the cover member 66, atransparent substrate (or transparent film) having the same area as theactive matrix substrate 61 may be used. Thus, in the state of FIG. 11B,it is used as the cover member common to all the active matrix portions.

[0160] After the cover member 66 is bonded, the active matrix cell isdivided into parts. In this embodiment, when the active matrix substrate61 and the cover member 66 are divided into parts, a scriber is used.The scriber is such a device that after a thin groove (scribe groove) isformed in the substrate, shock is given to the scribe groove to generatea crack along the scribe groove so that the substrate is divided intoparts.

[0161] Incidentally, as a device for dividing a substrate into parts, adicer is also known. The dicer is such a device that a hard cutter (alsoreferred to as dicing saw) is rotated at high speed and is put to asubstrate to divide it into parts. However, when the dicer is used,water is jetted to the dicing saw to prevent heat generation and splashof abrasive powder. Thus, in the case where the EL display device isfabricated, it is desirable to use the scriber, which does not usewater.

[0162] As the sequence of forming the scribe groove in the active matrixsubstrate 61 and the cover member 66, first, a scribe groove 67 a isformed in the direction of the arrow (a), and next, a scribe groove 67 bis formed in the direction of the arrow (b). At this time, the scribegroove passing through the vicinity of the opening portion 63 is formedto cut the first seal member 62. By doing so, since the opening portion63 appears at the end face of the active matrix cell, a subsequentinjection step of a filler is facilitated.

[0163] When the scribe grooves are formed in this way, a shock is givento the scribe grooves by an elastic bar of silicone resin or the like togenerate cracks, so that the active matrix substrate 61 and the covermember 66 are divided into parts.

[0164]FIG. 12A shows the state after the first division, and activematrix cells 68 and 69 each including two active matrix portions areformed through the division. Next, a filler 70 is injected into a spaceformed of the active matrix substrate 61, the first seal member 62 andthe cover member 66 by a vacuum injection method. Since the vacuuminjection method is well known as a technique of injecting liquidcrystal, its explanation is omitted. At this time, it is preferable thatthe viscosity of the filler 70 is 3 to 15 cp. The filler having suchviscosity may be selected, or desired viscosity may be made by dilutionwith a solvent or the like. Besides, the vacuum injection method may becarried out in the state where a drying agent is added in the filler.

[0165] In this way, the filler 70 is filled as shown in FIG. 12A.Incidentally, although this embodiment shows a system in which thefiller 70 is filled into the plurality of active matrix cells at thesame time, the system like this is suitable for fabrication of a smallEL display device with a diagonal of about 0.5 to 1 inch. On the otherhand, when a large EL display device with a diagonal of about 5 to 30inches is fabricated, it is appropriate that after division into therespective active matrix cells is made, the filler 70 is filled.

[0166] After the filler 70 is filled in the manner described above, thefiller 70 is hardened so that the adhesiveness between the active matrixsubstrate 61 and the cover member 66 is further raised. When the filler70 is an ultraviolet ray curing resin, ultraviolet rays are irradiated,and when it is a thermosetting resin, heating is made. However, in thecase where the thermosetting resin is used, attention must be paid tothe heat resistance of the organic EL material.

[0167] Next, scribe grooves are again formed in the active matrixsubstrate 61 and the cover member 66. As the sequence, first, a scribegroove 71 a is formed in the direction of the arrow (a), and next, ascribe groove 71 b is formed in the direction of the arrow (h). At thistime, the scribe grooves are formed so that the area of the cover member66 becomes smaller as compared with the active matrix substrate 61 afterthe division.

[0168] After the scribe grooves are formed in this way, a shock is givento the scribe grooves by an elastic bar of silicone resin or the like togenerate cracks, so that division into active matrix cells 72 to 75 ismade. FIG. 13A shows the state after the second division. Further, anFPC 76 is attached to each of the active matrix cells 72 to 75.

[0169] Finally, as shown in FIG. 13B, a second seal member 77 is formedso as to cover the substrate end face (exposed face of the first sealmember 62 or the filler 70) of each of the active matrix cells 72 to 75and the FPC 76. The second seal member 77 may be formed of anultraviolet ray curing resin or the like in which degassing hardlyoccurs.

[0170] By the process described above, the EL display device as shown inFIG. 13B is completed. As described above, by carrying out thisembodiment, a plurality of EL display devices can be fabricated from onesubstrate. For example, from a substrate of 620 mm×720 mm, six ELdisplay devices each having a diagonal of 13 to 14 inches can be formed,or four EL display devices each having a diagonal of 15 to 17 inches canbe formed. Thus, a throughput can be greatly improved and manufacturingcosts can be reduced.

[0171] Incidentally, the fabricating process of an EL display device ofthis embodiment can be used for fabrication of an EL display deviceincluding any structure of the embodiments 1 to 3.

[0172] [Embodiment 5]

[0173] In this embodiment, a description will be made on an example of acase where the filler 70 is not used in the embodiment 4. Thisembodiment is characterized in that after an active matrix cell isplaced in a vacuum, a dry. inert gas pressurized to 1 to 2 atmospheresis sealed in a region surrounded by the first seal member 62. As theinert gas, nitrogen or rare gas (typically argon, helium or neon) may beused.

[0174] Incidentally, this embodiment can use the process of theembodiment 4 as it is, except that a material vacuum injected in theembodiment 4 is made a gas. Thus, the fabricating process of the ELdisplay device of this embodiment can be used for fabrication of the ELdisplay device including any structure of the embodiments 1 to 3.

[0175] [Embodiment 6]

[0176] In the embodiments 1 to 5, although the description has been madeon the EL display device, the present invention can also be used for anactive matrix electrochromic display (ECD), field emission display(FED), or liquid crystal display (LCD).

[0177] That is, the present invention can be used for any electronicdevices in which a self light-emitting device or a light receivingelement is electrically connected to an TFT.

[0178] [Embodiment 7]

[0179] In Embodiment 1 laser crystallization is used for formationmethod of crystal silicon film 302, in this embodiment in the case ofusing another crystallization method is described.

[0180] After forming an amorphous silicon film in this embodiment,crystallization can be performed using the technique recorded inJapanese Patent Application Laid-open No. Hei 7-130652 or JapanesePatent Application Laid-open No. Hei 8-78329. The technique recorded inthe above patent applications is one of obtaining a crystalline siliconfilm having good crystallinity by using an element such as nickel as acatalyst for promoting crystallization.

[0181] Further, after the crystallization process is completed, aprocess of removing the catalyst used in the crystallization may beperformed. In this case, the catalyst may be gettered using thetechnique recorded in Japanese Patent Application Laid-open No. Hei10-270363 or Japanese Patent Application Laid-open No. Hei 3-330602.

[0182] In addition, a TFT may be formed using the technique recorded inthe specification of Japanese Patent Application Serial No. Hei11-076967 by the applicant of the present invention.

[0183] Note that it is possible to freely combine the constitution ofthe present embodiment with the constitution of any of embodiments 1 to6 in a case that an electronic device is produced.

[0184] [Embodiment 8]

[0185] In this embodiment, FIGS. 16A and 16B indicate image photographsof an EL display device which is fabricated by the present invention.FIG. 16A is an image photograph of an EL display device when a monomertype organic EL material is used as the light-emitting layer. Further,FIG. 16B is an image photograph of an EL display device produced when apolymer type organic EL material is used as the light-emitting layer.

[0186] [Embodiment 9]

[0187] The EL display device fabricated in accordance with the presentinvention is of the self-emission type, and thus exhibits more excellentrecognizability of the displayed image in a light place as compared tothe liquid crystal display device. Furthermore, the EL display devicehas a wider viewing angle. Accordingly, the EL display device can beapplied to a display portion in various electric apparatuses. Forexample, in order to view a TV program or the like on a large-sizedscreen, the EL display device in accordance with the present inventioncan be used as a display portion of an EL display (i.e., a display inwhich an EL display device is installed into a frame) having a diagonalsize of 30 inches or larger (typically 40 inches or larger.)

[0188] The EL display includes all kinds of displays to be used fordisplaying information, such as a display for a personal computer, adisplay for receiving a TV broadcasting program, a display foradvertisement display. Moreover, the EL display device in accordancewith the present invention can be used as a display portion of othervarious electric apparatuses.

[0189] Such electric apparatuses include a video camera, a digitalcamera, a goggles-type display (head mount display), a car navigationsystem, a sound reproduction device (an audio equipment), note-sizepersonal computer, a game machine, a portable information terminal (amobile computer, a portable telephone, a portable game machine, anelectronic book, or the like), an image reproduction apparatus includinga recording medium (more specifically, an apparatus which can reproducea recording medium such as a digital video disc (DVD), and includes adisplay for displaying the reproduced image), or the like. Inparticular, in the case of the portable information terminal, use of theEL display device is preferable, since the portable information terminalthat is likely to be viewed from a tilted direction is often required tohave a wide viewing angle. FIGS. 14A through 15B respectively showvarious specific examples of such electronic devices.

[0190]FIG. 14A illustrates an EL display which includes a frame 2001, asupport table 2002, a display portion 2003, or the like. The presentinvention is applicable to the display portion 2003. The EL display isof the self-emission type and therefore requires no back light. Thus,the display portion thereof can have a thickness thinner than that ofthe liquid crystal display device.

[0191]FIG. 14B illustrates a video camera which includes a main body2101, a display portion 2102, an audio input portion 2103, operationswitches 2104, a battery 2105, an image receiving portion 2106, or thelike. The EL display device in accordance with the present invention canbe used as the display portion 2102.

[0192]FIG. 14C illustrates a portion (the right-half piece) of an ELdisplay of head mount type, which includes a main body 2201, signalcables 2202, a head mount band 2203, a display portion 2204, an opticalsystem 2205, an EL display device 2206, or the like. The presentinvention is applicable to the EL display device 2206.

[0193]FIG. 14D illustrates an image reproduction apparatus including arecording medium (more specifically, a DVD reproduction apparatus),which includes a main body 2301, a recording medium (a DVD or the like)2302, operation switches 2303, a display portion (a) 2304, anotherdisplay portion (b) 2305, or the like. The display portion (a) is usedmainly for displaying image information, while the display portion (b)is used mainly for displaying character information. The EL displaydevice in accordance with the present invention can be used as thesedisplay portions (a) and (b). The image reproduction apparatus includinga recording medium further includes a CD reproduction apparatus, a gamemachine or the like.

[0194]FIG. 14E illustrates a portable (mobile) computer which includes amain body 2401, a camera portion 2402, an image receiving portion 2403,operation switches 2404, a display portion 2405, or the like. The ELdisplay device in accordance with the present invention can be used asthe display portion 2405.

[0195]FIG. 14F illustrates a personal computer which includes a mainbody 2501, a frame 2502, a display portion 2503, a key board 2504, orthe like. The EL display device in accordance with the present inventioncan be used as the display portion 2503.

[0196] When the brighter luminance of light emitted from the EL materialbecomes available in the future, the EL display device in accordancewith the present invention will be applicable to a front-type orrear-type projector in which light including output image information isenlarged by means of lenses or the like to be projected.

[0197] The aforementioned electronic devices are more likely to be usedfor display information distributed through a telecommunication pathsuch as Internet, a CATV (cable television system), and in particularlikely to display moving picture information. The EL display device issuitable for displaying moving pictures since the EL material canexhibit high response speed. However, if the contour between the pixelsbecomes unclear, the moving pictures as a whole cannot be clearlydisplayed. Since the EL display device in accordance with the presentinvention can make the contour between the pixels clear, it issignificantly advantageous to apply the EL display device of the presentinvention to a display portion of the electronic devices.

[0198] A portion of the EL display device that is emitting lightconsumes power, so it is desirable to display information in such amanner that the light emitting portion therein becomes as small aspossible. Accordingly, when the EL display device is applied to adisplay portion which mainly displays character information, e.g., adisplay portion of a portable information terminal, and more particular,a portable telephone or a sound reproduction equipment, it is desirableto drive the EL display device so that the character information isformed by a light-emitting portion while a non-emission portioncorresponds to the background.

[0199] With now reference to FIG. 15A, a cellular telephone isillustrated, which includes a main body 2601, an audio output portion2602, an audio input portion 2603, a display portion 2604, operationswitches 2605, and an antenna 2606. The EL display device in accordancewith the present invention can be used as the display portion 2604. Thedisplay portion 2604 can reduce power consumption of the portabletelephone by displaying white-colored characters on a black-coloredbackground.

[0200]FIG. 15B illustrates a sound reproduction device, a car audioequipment in concrete term, which includes a main body 2701, a displayportion 2702, and operation switches 2703 and 2704. The EL displaydevice in accordance with the present invention can be used as thedisplay portion 2702. Although the car audio equipment of the mount typeis shown in the present embodiment, the present invention is alsoapplicable to an audio of the set type. The display portion 2702 canreduce power consumption by displaying white-colored characters on ablack-colored background, which is particularly advantageous for theaudio of the portable type.

[0201] As set forth above, the present invention can be appliedvariously to a wide range of electric apparatuses in all fields. Theelectronic device in the present embodiment can be obtained by utilizingan EL display device having the configuration in which the structures inEmbodiments 1 through 8 are freely combined.

[0202] According to the invention, it can be possible to omit thecapacitor which is conventionally used to hold the gate voltage of thecurrent control TFT, so that the effective light emission area per onepixel is greatly increased. Thus, an electronic device of bright imagedisplay can be obtained. Furthermore, an electric apparatus with highperformance is provided by using the electronic device as its displayportion.

What is claimed is:
 1. An electronic device comprising: a first thinfilm transistor; a second thin film transistor having: a gate electrode,a gate insulating film, at least an LDD region, wherein the gateelectrode of the second thin film transistor is electrically connectedto a drain wiring of the first thin film transistor; a self lightemitting element, wherein the self light emitting element iselectrically connected to a drain wiring of the second thin filmtransistor, wherein the second thin film transistor is a p-channel thinfilm transistor, wherein at least a portion of the LDD region of thesecond thin film transistor is overlapped with the gate electrode withthe gate insulating film interposed therebetween.
 2. An electronicdevice comprising: a first thin film transistor; a second thin filmtransistor having: a gate electrode, a gate insulating film, at least anLDD region, wherein the gate electrode of the second thin filmtransistor is electrically connected to a drain wiring of the first thinfilm transistor; a self light emitting element, wherein the self lightemitting element is electrically connected to a drain wiring of thesecond thin film transistor, wherein the second thin film transistor isa p-channel thin film transistor, wherein at least a portion of the LDDregion of the second thin film transistor is overlapped with the gateelectrode with the gate insulating film interposed there between,wherein the first thin film transistor includes a plurality of thin filmtransistors being connected in series.
 3. An electronic devicecomprising a pixel portion and a driver circuit portion, said electronicdevice comprising: an n-channel thin film transistor being formed in thedriver circuit portion, said n-channel thin film transistor having: afirst gate electrode, a first gate insulating film, at least a first LDDregion, wherein the first LDD region is overlapped with the first gateelectrode with the first gate insulating film interposed therebetween, afirst thin film transistor being formed in the pixel portion; a secondthin film transistor being formed in the pixel portion, said second thinfilm transistor having: a second gate electrode, a second gateinsulating film, at least a second LDD region, a self light emittingelement being formed in the pixel portion, wherein the self lightemitting element is electrically connected to the second thin filmtransistor, wherein the second thin film transistor is a p-channel thinfilm transistor, wherein at least a portion of the second LDD region ofthe second thin film transistor is overlapped with the second gateelectrode with the second gate insulating film interposed therebetween.4. An electronic device comprising a pixel portion and a driver circuitportion, said electronic device comprising: an n-channel thin filmtransistor being formed in the driver circuit portion, said n-channelthin film transistor having: a first gate electrode, a first gateinsulating film, at least a first LDD region, wherein the first LDDregion is overlapped with the first gate electrode with the first gateinsulating film interposed therebetween, a first thin film transistorbeing formed in the pixel portion; a second thin film transistor beingformed in the pixel portion, said second thin film transistor having: asecond gate electrode, a second gate insulating film, at least a secondLDD region, a self light emitting element being formed in the pixelportion, wherein the self light emitting element is electricallyconnected to the second thin film transistor, wherein the second thinfilm transistor is a p-channel thin film transistor, wherein at least aportion of the second LDD region of the second thin film transistor isoverlapped with the second gate electrode with the second gateinsulating film interposed therebetween, wherein the first thin filmtransistor includes a plurality of thin film transistors being connectedin series.
 5. A device according to claim 1, wherein the LDD region ofthe second thin film transistor includes a p-type impurity element at aconcentration in a range of 1×10¹⁵ to 5×10¹⁷ atoms/cm³.
 6. An electricapparatus using the electronic device of claim
 1. 7. A device accordingto claim 2, wherein the LDD region of the second thin film transistorincludes a p-type impurity element at a concentration in a range of1×10¹⁵ to 5×10¹⁷ atoms/cm³.
 8. An electric apparatus using theelectronic device of claim
 2. 9. A device according to claim 3, whereinthe second LDD region of the second thin film transistor includes ap-type impurity element at a concentration in a range of 1×10¹⁵ to5×10¹⁷ atoms/cm³.
 10. An electric apparatus using the electronic deviceof claim
 3. 11. A device according to claim 4, wherein the second LDDregion of the second thin film transistor includes a p-type impurityelement at a concentration in a range of 1×10¹⁵ to 5×10¹⁷ atoms/cm³. 12.An electric apparatus using the electronic device of claim 4.